DYNAMICS OF INTELLIGENT POLY(N-ISOPROPYLACRYLAMIDE) MICROGELS

This dissertation investigates the self assembly and automatic oscillation of intelligent poly (N-isopropylacrylamide) [PNIPAM] microgel particles. The equilibrium phase diagram as a function of temperature and concentration was constructed for the charged PNIPAM spheres. The PNIPAM microgel particles display rhythmic size oscillations when covalently coupled to a nonlinear chemical reaction, the Belousov-Zhabotinsky (BZ) reaction. The nonequilibrium dynamics of PNIPAM microgels in the presence of BZ reaction was studied by the systematic variation of substrate concentrations and temperature. In addition, the BZ chemical reaction was modeled to reveal the existence of upper temperature limits for nonlinear chemical systems. The experiments employ environment sensitive PNIPAM particles that are sensitive to temperature, pH, and ionic strength. The PNIPAM particles have been demonstrated here to behave as hard spheres at low pH values and soft spheres at high pH. This is done by measuring the freezing and melting boundary of fluid-crystal coexistence region with a new technique which is simpler and quicker compared to the traditional sedimentation method. A novel method was developed to achieve size uniformity of PNIPAM gel particles with covalently-bound tris(bipyridyl)ruthenium(II) via the coordination chemistry between a ruthenium complex and the monodispersed PNIPAM gel particles bearing bipyridine ligands. The correlation between the dynamic behavior of BZ reaction induced mechanical oscillations of PNIPAM particles and substrate concentrations was presented in a ternary phase diagram. In particular, the dependence of oscillation frequency and induction time on the substrate concentrations was studied. The temperature dependency of the induction time and oscillatory frequency of the BZ reaction in this polymerimmobilized catalyst system were compared to the bulk BZ reaction with the catalyst in the solution phase. Prolonged induction times were observed for the immobilized catalyst, compared with free catalyst, while little difference was observed on the oscillation frequency. A theoretical improvement has been achieved by incorporating the temperature dependence in the BZ Oregonator model. Bifurcation has been calculated in the phase space spanned by initial reagents concentration ratio, stoichiometric factor and temperature. The existence of upper temperature limits has been demonstrated.